Conventionally, a magnetic rotation angle sensor, which senses a rotation angle of a detection target by rotating one of a magnet and a magnet detection device together with a detection target, to detect a magnetic flux direction variation or a magnetic flux density, is proposed (refer to U.S. Pat. No. 6,646,435 and its counterpart JP-2001-91208-A, which are referred to as Reference 1 in the following, and U.S. Pat. No. 6,137,288, U.S. Pat. No. 6,417,664, U.S. Pat. No. 6,472,865, U.S. Pat. No. 6,509,734, U.S. Pat. No. 6,956,368 and their counterpart JP-3411523-B2, which are referred to as Reference 2 in the following, for example).
In the magnetic rotation angle sensor according to Reference 1, a magnetic detection device is installed on an inner circumferential side of a magnet that is magnetized in a radial direction of a turning circle of a detection target, to be shifted from a center of the turning circle. A yoke covers outer circumferences of the magnet and the magnetic detection device. A rotation angle range of the detection target, in which the output of the magnetic detection device is linear, is extended by decreasing an angle of the magnetic flux, which is detected by the magnetic detection device, relative to the rotation angle of the detection target.
In the magnetic rotation angle sensor according to Reference 2, a magnetic flux density detection device rotates together with a detection target, and is installed on a radially shifted position from a rotation center, relative to a magnet that is formed in a substantially semicircular shape and magnetized in a radial direction of a turning circle of the detection target. Then, the magnetic flux density detection device detects the magnetic flux density that varies in accordance with a rotation of the semicircular magnet, to sense a rotation angle of the detection target.
However, as shown in FIG. 12, in the magnetic rotation angle sensor according to Reference 1, when a magnetoresistive device is used as the magnetic detection device, the rotation angle can be detected only in a range smaller than 180 degrees at the maximum, even if the output of the magnetoresistive device is linear over an extended rotation angle range. When a Hall effect device is used as the magnetic flux density detection device, the magnetic flux angle is calculated with a ratio between outputs of two Hall effect devices. This construction increases the number of parts, and raises a manufacturing cost. Further, the magnetic rotation angle sensor has such a magnetic circuit construction that the magnetic detection device is installed on the inner circumferential side of the magnet and the yoke covers the outer circumferences of the magnet and the magnetic detection device. Accordingly, the magnet is closer to the yoke than the magnetic detection device is. The magnetic flux generated by the magnet flows much toward the yoke than toward the magnetic detection device in this magnetic circuit construction, to cause an issue to decrease an output level of the magnetic detection device. The magnetic flux quantity generated by the magnet can be increased by forming the magnet in a large size, however, this causes another issue to upsize an entire size of the magnetic rotation angle sensor.
The magnetic rotation angle sensor according to Reference 2 does not extend a rotation angle range of the detection target in which the output of the magnetic detection device is linear, differently from Reference 1. That is, as shown in a voltage sensing signal waveform graph of FIG. 4B or 3B of Reference 2, the rotational angle range of the detection target, in which the output of the magnetic detection device is linear to be detected by the magnetic flux density detection device, is smaller than 180 degrees. Further, the magnetic flux density detection device is installed on a rotation path of the semicircular magnet, so that the magnetic flux density detection device hinders a movement of the magnet. Thus, the rotation angle range of the magnet is mechanically limited.